Throughout this application, various publications are referenced to by arabic numerals within parentheses. Disclosures of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this invention pertains. Full bibliographic citations for these references may be found at the end of this application, preceding the claims.
Gene therapy was proposed approximately 20 years ago as a way to ameliorate genetic defects by providing a source for missing essential genetic components. The injection of copies of the gene responsible for the production of a specific protein directly into the targeted area by means of a viral vector was considered a mode of insuring that the protein required would be synthesized at the site where it was needed. This approach offered a distinct advantage over prior conventional treatment of metabolic diseases, which required continuous injection of gene product from exogenous sources.
The principle behind gene therapy is simple; however, practical application has been difficult. Failure of early gene therapy was mainly due to three problems. Firstly, there were difficulties in efficiently transducing primary quiescent human cells in vivo. Secondly, there were strong immune responses to the gene therapy vectors, as well as to the foreign therapeutic transgenes that rapidly eliminated trans-gene expressing cells in humans. Thirdly, there was an ability of many cell types to shut off the viral promoters that controlled transgene expression in humans.
One positive outcome of these early efforts of gene therapy was the demonstration that introducing cloned genes into humans could be safe, with little or no morbidity. More recently, new vectors have been engineered, including adenoviruses and even naked DNA, enhancing the efficiency of in vivo gene delivery and reducing the immunogenicity of vectors and transgenes.
There is a need for a safer, more effective, and more precise method of gene therapy.